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  1. JDK
  2. JDK-8275405

Linking error for classes with lambda template parameters and virtual functions

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Details

    • Bug
    • Status: Resolved
    • P4
    • Resolution: Fixed
    • None
    • 18
    • infrastructure
    • b21

    Description

      We encountered the following linking error when trying to build Generational ZGC on Windows:
      ```
      jvm.exp : error LNK2001: unresolved external symbol "const ZBasicOopIterateClosure<class <lambda_9767402e468f9fc654281195f9700e48> >::`vftable'" (??_7?$ZBasicOopIterateClosure@V<lambda_9767402e468f9fc654281195f9700e48>@@@@6B@)
      ```

      I narrowed this down to a simple reproducer, which doesn't link when built through the HotSpot build system:
      ```
      #include <functional>
      std::function<void()> = [](){};
      ```

      I found that we have a line in our make files that filters out symbols that contain the string vftable (though it checks the mangled name, so a bit hard to find):
      ```
      else ifeq ($(call isTargetOs, windows), true)
        DUMP_SYMBOLS_CMD := $(DUMPBIN) -symbols *.obj
        FILTER_SYMBOLS_AWK_SCRIPT := \
            '{ \
              if ($$7 ~ /??_7.*@@6B@/ && $$7 !~ /type_info/) print $$7; \
            }'
      ```

      The following line prints the vftable symbol if it doesn't contain the string 'type_info':
       if ($$7 ~ /??_7.*@@6B@/ && $$7 !~ /type_info/) print $$7;

      The printed values are added to a list of symbols that get filtered out of the mapfile, which is then passed to the linker.

      If I add a second exception for vftable symbols. This addition also checks if the symbol contains the string 'lambda', and not only type_info:
       if ($$7 ~ /??_7.*@@6B@/ && $$7 !~ /type_info/ && $$7 !~ /lambda/) print $$7;

      With this the code now compiles.

      I did an additional experiment where I completely removed this filtering of vftable symbols. When I did that the linker complained that we used more than 64K symbols.

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              stefank Stefan Karlsson
              stefank Stefan Karlsson
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                Created:
                Updated:
                Resolved: